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The Satellite Data System (SDS-1) was composed of two operational satellites that had supported near-real time communications between low altitude photographic intelligence satellites and ground control stations, making it a critical part of the US Air Force Satellite Communications (AFSATCOM) System. In particular, SDS-1 served as a communications link between the Air Force Satellite Control Facility at Sunnyvale, CA, and 7 remote tracking stations located at Vandenberg AFB, Hawaii, Guam, Nahe Island, Greenland, the UK, and Boston. Furthermore, the SDS-1 enabled almost two-way real-time command, control, and UHF communications in the polar region for Strategic Air Command (SAC) forces. The North polar region was not covered by communications satellites in geostationary orbit, and therefore the SDS-1 filled the gap. A third and unacknowledged function was to provide a relay for information from the KH-11 photo reconnaisance satellite to a ground station, which was probably the Defense Special Missile and Astronautics Center at Fort Meade, MD. It flew in 63 deg orbits, having high apogees over the North Pole and low perigees. This gave it a long stay time over the polar region, enabling it to relay communications to aircraft in those areas. Two of the SDS-1 satellites had to be in orbit for the communications to be constant. Each had 12 communications channels in the UHF band. The main transmitting antenna was over 10 feet in diameter. The body itself, based on the design of the TACSAT, was cylindrical and about 13 feet long and 10 feet in diameter. The outside cylinder, call the solar array, was made of a silicon skin and spun for thermal distribution of the heat load. The primary electrical power was provided by solar charged batteries with a total of 980 watts of power.

Alternate Names

  • 15226
  • SDSF-5A
  • Satellite Data System F-5A
  • USA 4

Facts in Brief

Launch Date: 1984-08-28
Launch Vehicle: Titan III-B
Launch Site: Vandenberg AFB, United States
Mass: 700 kg

Funding Agency

  • Department of Defense-Department of the Air Force (United States)


  • Surveillance and Other Military

Additional Information

Questions and comments about this spacecraft can be directed to: Coordinated Request and User Support Office

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